Impulse 3405 - Manual (Page 7)

Card Setup
Sealevel Systems VERSA COMM+4/EX Page 4
Jumper Selections
For ease of configuration, the headers are grouped by port. Port one headers
have a ‘J1’ prefix, Port two headers have the ‘J2’ prefix, etc. For example, the
header that controls the Port one IRQ selection is J1B, the header that controls
the Port 2 IRQ selection is J2B. The silk-screen also provides information for
configuring the adapter without the use of the manual. This is particularly useful
in field re-configuration.
IRQ Selection
Headers J1B through J4B select the interrupt request for each serial port. If
COM1: is selected, the corresponding jumper must be on the IRQ4 setting. If
COM2: is selected, the corresponding jumper must be on IRQ3. (This only
applies to the traditional DOS COM: port assignments, in Windows COM1: can
use I/O address 300 and IRQ15 if it is available!)
3 4 5 6 7 10 11 12 15 9
Figure 4 – Headers J1B – J4B, IRQ Selection
Note: Most DOS communications software applications default COM3: to IRQ4
and COM4: to IRQ3. This requires the sharing of interrupts between
COM1: and COM3:, and between COM2: and COM4:. While this is the
default, it is not always the preferred setting. Check your software
configuration instructions to determine the most appropriate IRQ
selection.
Any two or more ports can share a common IRQ by placing the jumpers on the
same IRQ setting and setting the appropriate selections at J1A through J4A.
When sharing IRQs, many operating systems (i.e. Windows NT) will require the
location of the Interrupt Status Port (ISP). Please see Page 10 for a description
of the ISP and how it is used.